Maybe I did not phrase the question correctly.
By "standard", I mean what makes the Spanish dollar "regular". As in what is the Spanish dollar regulated by?
For instance- the meter is regulated by the distance an object falls in a vacume in one second, this being precisely ten meters. A gram is regulated by the weight of one cubic centimeter volume of distilled water, this being precisely one gram, and a liter is a cubic decimeter or 1000 grams water.
Maybe the Spanish dollar was regulated by the weight of the queen of England's toe nail clippings collected for one year, I don't know. But there must have been a standard to keep all the Spanish dollars stamped out regular size or weight.
So what was it? I'm sure it wasn't as clever as the metric system, using constants such as gravity or specific volumes of water, but their must have been some kind of standard.
Edited to add-
Darn it! I was wrong about the meter, all the television satellite cable signals messing up my memory of high-shcool physics class with something else. The meter is based on one millionth of the distance from North Pole to South Pole.
Pfffft! My idea was better.... : )